The magnitude of proliferation was similar across groups: 25 subjects had an SI > 5 and 12 subjects had an SI > 10 at any time-point compared with baseline. Proliferative responses of greatest magnitude (SI > 10) across dose groups were elicited by HBcAg. The frequency of ASCA responders was low, although there were more responders in Cohort A (seven subjects, 12%) than Cohort B (one subject, 2%). There was also a slight trend toward higher IgA and IgG levels

in Cohort A. The total number of responders (IgA plus IgG) was the highest in Cohort A 80 YU (five subjects, 8%). Generally, IgA and IgG levels were low at baseline with only six subjects showing a baseline response ≥25 U. These low levels were maintained during treatment. Seven of the eight ASCA responders were also defined as responders in the ELISpot. In addition, for 80 YU, MLN0128 cost all ASCA responders also displayed ELISpot and LPA responses. No anti-HBcAg antibodies were detected at any time during the study and no anti-HBsAg antibody levels >8.4 IU/mL

were determined. Two subjects, both in Cohort A 80 YU, had anti-HBsAg levels ≥3.5 IU/L during the study. HLA testing was performed to evaluate for any HLA restriction of immune responses to GS-4774. The most frequent HLA alleles were A*02, C*07, DQB1*03, and DRB1*04. No association was found between common HLA alleles and the IFN-γ ELISpot Dinaciclib purchase response to peptides or recombinant antigens (Supplementary Table 7). In the present study, GS-4774 was generally safe and well-tolerated. The most common adverse events were injection-site reactions. Adverse events occurred more frequently in both cohorts of the highest dose group, 80 YU, and the number of individual adverse events was higher after weekly than monthly immunization. Immunization with GS-4774 led to HBV antigen-specific and treatment-emergent T-cell responses. The majority much of subjects showed a response when assessed by at

least one of the assays. GS-4774 was immunogenic at all three doses tested and both immunization regimens, weekly and monthly dosing, induced T-cell-mediated immune responses. Immunogenicity was independent of HLA alleles. LPA responses were observed in the majority of subjects with no increase in the frequency of responders related to dose or timing of dose. LPA responses were measured using recombinant HBV proteins which preferentially utilize an MHC Class II pathway resulting in a bias toward CD4+ T-cell activation [12]. The responses, therefore, may represent early CD4+ T-cell activation with GS-4774 in these subjects. The higher magnitude LPA responses with SI > 5, breadth of proliferative responses to recombinant antigens, and timing of response emergence suggested an increase in LPA responses from 10 to 40 YU doses but not from 40 to 80 YU. IFN-γ ELISpot responses were seen in fewer subjects and at later time-points than LPA responses.